1. Field of the Invention
The present invention relates to a recording disk reproducing apparatus, and particularly relates to an optical recording disk reproducing apparatus such as an optical video disk player, and the like.
2. Description of the Background Art
An optical recording disk reproducing apparatus reproduces recorded information on a recording surface of an information recording disk (hereinafter simply referred to as a disk) by using a pickup for radiating a light beam onto the recording surface as to detect the recorded information by means of, for example, reflected light from the recording surface. In such a recording disk reproducing apparatus, the pickup is movable in the radial direction of the disk, and the rotational driving of the disk is controlled by a spindle servo device, so that the movement of an information detecting light spot of the pickup relative to the disk is controlled.
The apparatus further is provided with a focusing servo device for controlling the position of the focus of the light beam of the pickup so as to form the information detecting light spot on the recording surface of the disk. The apparatus further is provided with a tracking servo device for controlling the light spot so as to make the light spot accurately trace a recording track which is formed on the recording surface, for example, spirally.
There has been proposed a recording disk reproducing apparatus employing a so-called digital servo device for generating an error signal corresponding to a difference between a target value and a control amount on the basis of the output signal of the pickup so as to perform phase compensation, or the like, of the error signal in a digital manner. In such an apparatus, an A/D (analog-to-digital) converter for converting the analog error signal into a digital one is used. The higher the number of bits of the output data of the A/D converter, the higher the resolution, so that highly accurate controlling can be performed. However, as a result, the operational processing becomes complicated and the required processing time increases, so that the sampling frequency cannot be made sufficiently high. Consequently, there is deterioration of the phase characteristic of the servo, making stability poor as well as resulting in an increase in the number of the constituent elements of the A/D converter, thereby increasing the cost.
For the foregoing reasons, the conventional recording disk reproducing apparatus using a digital servo device is disadvantageous in that it is impossible to perform stable control with high accuracy, and in that the cost is high.